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Sinking rates responses of oceanic phytoplankton to irradiance, nutrients, and iron stress Lecourt, Maude
Abstract
Emiliania huxleyi (Lohmann), a small oceanic coccolithophore, was isolated from the NE Subarctic Pacific Ocean. The sinking rates of two strains of E. huxleyi, naked and coccolith-forming, were measured. The two strains were grown under saturating and lightlimited conditions in media containing either NO3 or NH4 as the primary nitrogen source. Sinking rates were measured during log and senescent growth phases. The naked strain grew significantly faster under saturating light than the coccolith-forming strain. The coccolith-forming strain of E. huxleyi had a significantly larger cell volume and higher sinking rates than the naked strain under all conditions. The naked strain increased significantly its chi a content under light limitation. POC and PUN were significantly higher for the coccolith-forming strain. During senescence, coccolith formation and cell aggregation increased for the coccolith-forming strain and the naked strain, respectively, significantly increasing their sinking rates. No significant difference in physiological parameters was observed between NO3 and NH4+ grown cells, except that growth rate was faster under NH4 at saturating light. These results suggest that coccolith formation controls sinking rates, and therefore the coccolith-forming strain has some advantages over the naked strain. This study also determined the sinking rates responses, physiological parameters, and iron quotas of E. huxleyi (coccolith forming strain) and an oceanic strain of the diatom Actinocyclus sp. (20 im diameter) under iron deficiency. Actinocyclus sp. was grown under N03- and N4+H to determine whether there was an advantage for cells to grow on NH4 rather than NO3- under iron-deplete conditions. E. huxleyi was grown on NO3- only. Under iron-deficient conditions, Actinocyclus sp. increased its sinking rate 9 fold, despite its 30% decrease in cell volume. E. huxleyi maintained its sinking rates, but deceased its cell volume by 50%. Growth rates and iron quotas of Actinocyclus sp. and E. huxleyi significantly decreased under iron-deplete conditions. E. huxleyi maintained its POC and PUN and increased its chi a content under iron-deplete conditions. On the other hand, Actinocyclus sp. significantly decreased its POC, PON and its chi a content when grown on N03. The results obtained under iron-deplete conditions indicate that E. huxleyi grown on N0 3 was not significantly affected by iron stress. However, Actinocyclus sp. was affected by iron deficiency, and was energetically affected by the nitrogen source. Finally, small coccolithophores are better adapted to their habitat (i.e. low iron concentrations in the NE Subarctic Pacific) and can easily outcompete large diatoms in a low iron environment.
Item Metadata
Title |
Sinking rates responses of oceanic phytoplankton to irradiance, nutrients, and iron stress
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
1994
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Description |
Emiliania huxleyi (Lohmann), a small oceanic coccolithophore,
was isolated from the NE Subarctic Pacific Ocean. The sinking rates
of two strains of E. huxleyi, naked and coccolith-forming, were
measured. The two strains were grown under saturating and lightlimited
conditions in media containing either NO3 or NH4 as the
primary nitrogen source. Sinking rates were measured during log
and senescent growth phases. The naked strain grew significantly
faster under saturating light than the coccolith-forming strain. The
coccolith-forming strain of E. huxleyi had a significantly larger cell
volume and higher sinking rates than the naked strain under all
conditions. The naked strain increased significantly its chi a content
under light limitation. POC and PUN were significantly higher for the
coccolith-forming strain. During senescence, coccolith formation and
cell aggregation increased for the coccolith-forming strain and the
naked strain, respectively, significantly increasing their sinking rates.
No significant difference in physiological parameters was observed
between NO3 and NH4+ grown cells, except that growth rate was
faster under NH4 at saturating light. These results suggest that
coccolith formation controls sinking rates, and therefore the
coccolith-forming strain has some advantages over the naked strain.
This study also determined the sinking rates responses,
physiological parameters, and iron quotas of E. huxleyi (coccolith
forming strain) and an oceanic strain of the diatom Actinocyclus sp.
(20 im diameter) under iron deficiency. Actinocyclus sp. was grown
under N03- and N4+H to determine whether there was an advantage
for cells to grow on NH4 rather than NO3- under iron-deplete
conditions. E. huxleyi was grown on NO3- only. Under iron-deficient
conditions, Actinocyclus sp. increased its sinking rate 9 fold, despite
its 30% decrease in cell volume. E. huxleyi maintained its sinking
rates, but deceased its cell volume by 50%. Growth rates and iron
quotas of Actinocyclus sp. and E. huxleyi significantly decreased
under iron-deplete conditions. E. huxleyi maintained its POC and PUN and increased its chi a content under iron-deplete conditions. On the
other hand, Actinocyclus sp. significantly decreased its POC, PON and
its chi a content when grown on N03. The results obtained under
iron-deplete conditions indicate that E. huxleyi grown on N0 3 was
not significantly affected by iron stress. However, Actinocyclus sp.
was affected by iron deficiency, and was energetically affected by
the nitrogen source. Finally, small coccolithophores are better
adapted to their habitat (i.e. low iron concentrations in the NE
Subarctic Pacific) and can easily outcompete large diatoms in a low
iron environment.
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Extent |
2021471 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-03-03
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0053333
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
1994-11
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.